Sildenafil timeline?

Here’s a concise development/regulatory timeline for sildenafil:

- 1989–1990: Pfizer scientists identify sildenafil citrate while screening compounds for cardiovascular use; found to be a potent PDE5 inhibitor.
- Early to mid-1990s: Preclinical and early clinical testing; erectile dysfunction (ED) side effects begin to emerge, suggesting a potential ED indication.
- 1998: FDA approves sildenafil citrate for erectile dysfunction (brand name Viagra); becomes the first oral medication specifically for ED.
- 2005: FDA approves sildenafil for pulmonary arterial hypertension (PAH) under the brand Revatio (to improve exercise ability in PAH).
- 2010s: Patent protection around sildenafil’s ED indication begins to expire in many markets; generic versions enter various markets (US and elsewhere) starting around 2012–2013, increasing competition and lowering costs.
- Late 2010s–present: Sildenafil remains widely used for ED and PAH; ongoing generic availability and continued regulatory use worldwide.

If you want, I can tailor this to a specific country or focus on patent/generic timelines in more detail.